There is a well known Brooks Robinson prototype card that you cansee in the links linked above but Xograph/Visual Panographics also created a Football (Soccer) prototype that is equally as rare:
Love that team font! The player depicted is actually a Brazilian named Jarbas Faustinho who player for Napoli from 1962-63 through 1968-69 before departing for three years. The back is blank but stamped in similar fashion to may baseball 3-D's:
Compare that to the stamps on the baseball versions (which are pre-production and not a prototype like the Robinson, which is unstamped):
As you can plainly see, the stamp is contained within the dimensions of the baseball version but not so on the soccer card. Ergo, it must be a tad tinier but I'm not so sure. It also appears that the back of the soccer card uses a font made up of dots, possibly from a dot matrix printer, while the blurriness of the baseball example above looks like a true rubber stamp was used.
It's a neat piece and like the Robinson prototype the number of extant examples can surely be counted on one hand. Both the Robinson prototype and this card are said to come from an old Xograph employee so it looks some examples were returned to them after all!